This invention relates in general to semiconductor electromechanical devices, and in particular to a microvalve device for controlling an automatic transmission.
MEMS (MicroElectroMechanical Systems) is a class of systems that are physically small, having features with sizes in the micrometer range. These systems have both electrical and mechanical components. The term xe2x80x9cmicromachiningxe2x80x9d is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices. MEMS originally used modified integrated circuit (computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micromachine these very small mechanical devices. Today there are many more micromachining techniques and materials available. The term xe2x80x9cmicrovalvexe2x80x9d as used in this application means a valve having features with sizes in the micrometer range, and thus by definition is at least partially formed by micromachining. The term xe2x80x9cmicrovalve devicexe2x80x9d as used in this application means a device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micromachined components or standard sized (larger) components.
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member or valve movably supported by a body and operatively coupled to an actuator for movement between a closed position and a fully open position. When placed in the closed position, the valve blocks or closes a first fluid port that is placed in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the valve moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports. Co-pending U.S. patent application Ser. No. 09/532,604, entitled xe2x80x9cPilot Operated Microvalve Devicexe2x80x9d, describes a microvalve device consisting of an electrically operated pilot microvalve and a pilot operated microvalve who position is controlled by the pilot microvalve.
In addition to generating a force sufficient to move the displaced member, the actuator must generate a force capable of overcoming the fluid flow forces acting on the displaceable member that oppose the intended displacement of the displaced member. These fluid flow forces generally increase as the flow rate through the fluid ports increases.
The invention relates to an electronically controlled automatic transmission and a microvalve device suitable for controlling fluid flow in a fluid control circuit of an electronically controlled automatic transmission. The electronically controlled automatic transmission includes an input shaft, an output shaft, and a plurality of gears providing driving connection between the input shaft and the output shaft. The electronically controlled automatic transmission further includes at least one hydraulically operated component, such as a hydraulically operated brake band, or a hydraulically operated clutch, which is operable to effect a change in the gear reduction provided by the gears between the input shaft and the output shaft. A source of pressurized hydraulic fluid is provided to operate the hydraulically operated components of the electronically controlled automatic transmission. A microvalve device according to the invention is selectively operable to control passage of pressurized hydraulic fluid from the source to the hydraulically operated component. The microvalve device, in a preferred embodiment, includes a pilot-operated valve for controlling and selectively preventing the flow of pressurized hydraulic fluid to the hydraulically operated component. The microvalve device also includes an electronically controlled pilot valve for controlling the flow of pressurized hydraulic fluid to the slider valve to control the operation of the slider valve.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.